Generally, wireless local area networks (WLAN) use the IEEE 802.11 Protocol. A wireless local area network is generally includes one access point (Access Point, AP) and at least one station (Station, STA). The IEEE 802.11 Protocol includes many protocol branches, such as 802.11a, 802.11b, 802.11g and 802.11n, and different protocol branches have different application scenarios or service application types. For example, bandwidths for data transmission are different: 802.11n can support a bandwidth of 40 MHz, and each of 802.11a, 802.11b and 802.11g can support a bandwidth of 20 MHz; operating frequency bands are different, the numbers of antennas that can be supported for transmission are different, supported modulation and coding modes are different, and the like.
When an 11n system is designed, backward compatibility is considered. That is, STAs that support 802.11a, 802.11b and 802.11g can still be connected to an 11n system (that is, an 11n local area network) for communication as if they were connected to their respective systems, that is, the STAs that support 802.11a, 802.11b and 802.11g do not know that they are actually connected to an 802.11n system. However, when the STAs that support 802.11a, 802.11b and 802.11g communicate, by using the 802.11n system, with an AP that supports 802.11n, features of 802.11n cannot be used. This is because the bandwidth supported by 802.11n is 40 MHz, and the bandwidth supported by 802.11a, 802.11b and 802.11g is 20 MHz; and when communicating, by using the 802.11n system, with the AP that supports 802.11n, the STAs that support 802.11a, 802.11b and 802.11g occupy only 20 MHz of the 40 MHz for communication, and the other 20 MHz of the bandwidth is wasted consequently.
In a process of studying and practicing the prior art, the inventor of the present invention finds that during communication, by using the 802.11n system, with the AP that supports 802.11n, the STAs that support 802.11a, 802.11b and 802.11g occupy only 20 MHz of the 40 MHz for communication, and the other 20 MHz of the bandwidth is wasted consequently, which reduces a network throughput, and further reduces a utilization rate of spectrum resources.